A polyimide film and its preparation method

Abstract

This invention relates to the field of polymer materials technology, specifically to a polyimide film and its preparation method. The method includes mixing 3,3',4,4'-benzophenone tetracarboxylic dianhydride, methanol, and N,N-dimethylformamide, and performing an esterification reaction to obtain an esterified anhydride solution; mixing 4,4'-diaminobenzophenone and the esterified anhydride solution, adding N,N-dimethylformamide, and performing a polycondensation reaction to obtain a polyamic acid precursor solution; mixing the polyamic acid precursor solution, a crosslinking agent, a catalyst, and a dehydrating agent, and performing a chemical imidization reaction; coating the chemically imidized solution onto a substrate, and sequentially performing drying, pre-curing, and curing to obtain the polyimide film. The polyimide film prepared by this method exhibits excellent performance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a polyimide film and its preparation method. Background Technology

[0002] Polyimide (PI) films are widely used in flexible copper-clad laminates, aerospace insulation layers, and special motor slot insulation due to their excellent high-temperature resistance, mechanical strength, and electrical insulation properties. Traditional PI films are mostly prepared using a two-step method: first, dianhydride and diamine are polymerized at low temperature to produce polyamic acid (PAA), and then the ring is closed by high-temperature stepwise thermal imidization at temperatures above 300°C.

[0003] The existing technology has the following defects: (1) Thermal imidization requires high temperature and long baking time, which can easily lead to stress concentration, wrinkling and microcracks in the film, and high energy consumption; (2) Although conventional chemical imidization can close the ring at room temperature, it often causes side reactions or chain breakage due to excessive dehydrating agent (acetic anhydride), or insufficient imidization due to improper catalyst ratio. For example, Chinese patent CN103665426B, a chemical imidization preparation method for polyimide film, does not involve the control of esterified acid anhydride and specific molar ratio, and the film is prone to brittle cracking; (3) Chinese patent CN105419053A, polyimide film and its preparation method, discloses the addition of end capping agent to control molecular weight, but does not solve the influence of solid content and catalytic system synergy on film formation and thermal stability.

[0004] In summary, there is an urgent need for a method to prepare PI films that can achieve high imidization, good film-forming properties, and excellent thermal stability under mild conditions. Summary of the Invention

[0005] The present invention aims to solve the technical problem of how to provide a method for preparing PI films with high imidization degree, good film-forming properties and excellent thermal stability under mild conditions.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a polyimide film, comprising the following steps:

[0007] S1. Mix 3,3',4,4'-benzophenone tetracarboxylic dianhydride, methanol and N,N-dimethylformamide and carry out esterification reaction to obtain esterified anhydride solution;

[0008] S2. Mix 4,4'-diaminobenzophenone and esterified anhydride solution, add N,N-dimethylformamide, and carry out polycondensation reaction to obtain polyamic acid precursor solution;

[0009] S3. Mix the polyamic acid precursor solution, crosslinking agent, catalyst, and dehydrating agent to carry out a chemical imidization reaction;

[0010] S4. The solution after the chemical imidization reaction is coated onto the substrate, and then dried, pre-cured and cured in sequence to obtain the polyimide film.

[0011] A second aspect of the present invention provides a polyimide film prepared by the above-mentioned method, wherein the polyimide film has a 5wt% thermal weight loss temperature ≥570℃ and a carbon residue rate ≥60wt% under nitrogen atmosphere at 800℃.

[0012] The beneficial effects of this invention are as follows:

[0013] (1) The preparation method provided by the present invention uses esterified BTDA and DABP polycondensation to reduce the hydrolysis sensitivity of dianhydride. The polyamic acid PAA solution has excellent stability. The molar ratio of catalyst and dehydrating agent is 1:0.5. 20wt% solid content is combined with 2% crosslinking agent. FT-IR characterization confirms that the 1655cm⁻¹ crosslinking agent is 1655cm⁻¹. -1 The residual PAA peaks have largely disappeared, indicating the highest degree of imidization.

[0014] (2) The polyimide film provided by the present invention begins to decompose at 550°C, has a thermal weight loss temperature of 5wt% ≥570°C, a carbon residue rate of ≥60wt% under nitrogen atmosphere at 800°C, and a polyimide solution viscosity of 120~180mPa·s. The film is smooth, crack-free, and flexible.

[0015] (3) The highest temperature of the entire preparation method provided by the present invention is ≤180℃, which is significantly lower than that of the thermal imidization process, saving energy and reducing thermal defects. Detailed Implementation

[0016] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0017] In this invention, the inventors discovered that if 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) is first esterified with methanol and then polycondensed with 4,4'-diaminobenzophenone (DABP), and then chemically imidized under specific solid content, specific catalyst triethylamine molar ratio to dehydrating agent propionic anhydride, and specific crosslinking agent conditions, a fully imidized, flexible, defect-free PI film with excellent heat resistance can be obtained.

[0018] The first aspect of this invention provides a method for preparing a polyimide film, comprising the following steps:

[0019] S1. Mix 3,3',4,4'-benzophenone tetracarboxylic dianhydride, methanol and N,N-dimethylformamide and carry out esterification reaction to obtain esterified anhydride solution;

[0020] S2. Mix 4,4'-diaminobenzophenone (DABP) and esterified anhydride solution, add N,N-dimethylformamide, and carry out polycondensation reaction to obtain polyamic acid (PAA) precursor solution;

[0021] S3. Mix the polyamic acid precursor solution, crosslinking agent, catalyst, and dehydrating agent to carry out a chemical imidization reaction;

[0022] S4. The solution after the chemical imidization reaction is coated onto the substrate, and then dried, pre-cured and cured in sequence to obtain the polyimide film.

[0023] According to the present invention, in step S1, the molar ratio of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, methanol and N,N-dimethylformamide is 1:2:6~32.

[0024] According to a preferred embodiment of the present invention, the molar ratio of BTDA to methanol is 1:2.

[0025] According to the present invention, the conditions for the esterification reaction include: the temperature of the esterification reaction is 55~65°C, and the time of the esterification reaction is 3~4 hours.

[0026] According to the present invention, in step S2, the molar amounts of 4,4'-diaminobenzophenone and 3,3',4,4'-benzophenone tetracarboxylic dianhydride are the same.

[0027] According to the present invention, the conditions for the polycondensation reaction include: the temperature of the polycondensation reaction is 75~85°C, and the time of the polycondensation reaction is 5~7h.

[0028] According to the present invention, in step S2, N,N-dimethylformamide is added to make the solid content of the reaction system 18~22wt%.

[0029] According to the present invention, in step S3, the crosslinking agent is 1,3,5-tris(4-aminobenzene)benzene.

[0030] According to the present invention, the catalyst is triethylamine.

[0031] According to the present invention, the dehydrating agent is propionic anhydride.

[0032] According to the present invention, in step S3, the molar amount of the crosslinking agent is 1.5 to 2.5% of the total amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 4,4'-diaminobenzophenone.

[0033] According to the present invention, the molar ratio of the crosslinking agent, catalyst, and dehydrating agent is 0.1~0.2:1:0.4~0.6.

[0034] According to a preferred embodiment of the present invention, the molar ratio of the catalyst to the dehydrating agent is 1:0.5.

[0035] According to the present invention, in step S3, the conditions for the chemical imidization reaction include: the temperature of the chemical imidization reaction is 20~30°C, and the time of the chemical imidization reaction is 10~14h.

[0036] According to a preferred embodiment of the present invention, in step S3, the mixing step includes: adding a crosslinking agent to a polyamic acid precursor solution and reacting for 0.5 to 1.5 hours, followed by adding a catalyst and a dehydrating agent.

[0037] According to the present invention, in step S4, the drying conditions include: holding at 70-90°C for 10-15 minutes.

[0038] According to the present invention, the pre-curing conditions include: holding at 140-160°C for 25-35 minutes.

[0039] According to the present invention, the curing conditions include: holding at 170-190°C for 25-35 minutes.

[0040] A second aspect of the present invention provides a polyimide film prepared by the above-mentioned method, wherein the polyimide film has a 5wt% thermal weight loss temperature ≥570℃ and a carbon residue rate ≥60wt% under nitrogen atmosphere at 800℃.

[0041] Test methods

[0042] In this invention, the 5wt% thermogravimetric temperature (T5) of the polyimide film is... d5％ The nitrogen carbon residue at 800℃ was measured using conventional methods in this field.

[0043] The method for testing the dynamic viscosity of polyimide solution after chemical imidization of polyamic acid (PAA) is as follows: the viscosity is measured using a viscometer at 3 rotors and 60 rpm.

[0044] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. All other embodiments implemented by those skilled in the art based on the embodiments of the present invention without creative improvements are within the protection scope of the present invention.

[0045] The reagents used in the examples and comparative examples are conventional reagents in the art and are all commercially available.

[0046] Example 1

[0047] Add 3.000g (9.31 mmol) of BTDA, 0.597g (18.62 mmol) of methanol and 2.700g of DMF to a three-necked flask and stir magnetically at 60℃ for 3.5h until clear.

[0048] Add 2.006 g (9.31 mmol) of DABP and 18.540 g of DMF to make the solid content of the system 20 wt%. Heat the mixture to 80 °C and react for 6 h to obtain a PAA solution.

[0049] Add 0.010 g of crosslinking agent 1,3,5-tris(4-aminobenzene)benzene (2% of the total amount of diamine and dianhydride) to the PAA solution and react for 1 h. Then add 0.126 g (1.25 mmol) of triethylamine and 0.081 g (0.625 mmol) of propionic anhydride at a molar ratio of 1:0.5 and stir at 25 °C for 12 h.

[0050] After coating, the film was treated at 80℃ / 10min, 150℃ / 30min, and 180℃ / 30min, and then removed by water at 50℃. Polyimide film A1 was obtained.

[0051] The film is golden yellow, transparent, and flat, with a thickness of 25 μm.

[0052] Fourier transform infrared spectrum (FT-IR): 1777 cm⁻¹ -1 1720cm -1 Strong absorption, 1655cm -1 The peak is almost gone.

[0053] TG:T d5％ =576℃, 63.2% carbon residue at 800℃, dynamic viscosity 132mPa·s.

[0054] Comparative Example 1

[0055] Polyimide films were prepared according to the preparation method of Example 1, except that the amount of propionic anhydride was changed to 0.162 g, and the molar ratio of dehydrating agent to catalyst was 1:1.

[0056] Polyimide film DA1 was prepared.

[0057] The film was mostly intact but slightly brittle, FT-IR 1655cm -1 A weak peak is observed, with slightly lower imidization. Dynamic viscosity is 170 mPa·s. T d5% =565℃, residual carbon rate 60.1%.

[0058] Comparative Example 2

[0059] Polyimide films were prepared according to the preparation method of Example 1, except that 0.324 g of propionic anhydride was used and the molar ratio of dehydrating agent to catalyst was 1:2.

[0060] Polyimide film DA2 was prepared.

[0061] Microcracks appeared after the coating cured, and some areas curled. FT-IR 1655cm -1 Clearly, imidization is incomplete. d5% =552℃.

[0062] Comparative Example 3

[0063] Polyimide films were prepared according to the preparation method of Example 1, except that 0.504 g of propionic anhydride was used and the molar ratio of dehydrating agent to catalyst was 1:3.

[0064] Polyimide film DA3 was prepared.

[0065] Poor film formation, with multiple areas of powdering and cracking, making complete film removal impossible. FT-IR 1655cm -1 Strong, 1720cm -1 The peak is weak.

[0066] Comparative Example 4

[0067] Polyimide films were prepared according to the preparation method of Example 1, except that after esterification of BTDA 5.000g, methanol 1.000g, and DMF 4.500g, DABP 3.350g was added, and DMF was added to bring the solid content to 50wt%.

[0068] The precursor has extremely high viscosity, and it cracks and powders severely during curing after coating, making it impossible to obtain a continuous film.

[0069] Comparative Example 5

[0070] Polyimide films were prepared according to the preparation method of Example 1, except that no crosslinking agent was added.

[0071] Polyimide film DA5 was prepared.

[0072] The film can be formed, but its flexibility is slightly poor, and the edges are prone to micro-cracks when stretched. The TG residual carbon rate is 58.7%.

[0073] Comparative Example 6

[0074] Polyimide films were prepared according to the preparation method of Example 1, except that propionic anhydride was replaced with acetic anhydride.

[0075] Polyimide film DA6 was prepared.

[0076] Film formation is acceptable, but imidization is lower than in the propionic anhydride system. (T) d5％=568℃, residual carbon rate 60.8%.

[0077] By comparing the examples and comparative examples, it can be seen that the polyimide film provided by the present invention has excellent performance, specifically, a 5wt% thermal weight loss temperature ≥570℃ and a carbon residue rate ≥60wt% under nitrogen atmosphere at 800℃.

[0078] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a polyimide film, characterized in that, Includes the following steps: S1. Mix 3,3',4,4'-benzophenone tetracarboxylic dianhydride, methanol and N,N-dimethylformamide and carry out esterification reaction to obtain esterified anhydride solution; S2. Mix 4,4'-diaminobenzophenone and esterified anhydride solution, add N,N-dimethylformamide, and carry out polycondensation reaction to obtain polyamic acid precursor solution; S3. Mix the polyamic acid precursor solution, crosslinking agent, catalyst, and dehydrating agent to carry out a chemical imidization reaction; S4. The solution after the chemical imidization reaction is coated onto the substrate, and then dried, pre-cured and cured in sequence to obtain the polyimide film.

2. The method for preparing the polyimide film according to claim 1, characterized in that, In step S1, the molar ratio of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, methanol, and N,N-dimethylformamide is 1:2:6~32; The conditions for the esterification reaction include: a temperature of 55-65°C and a reaction time of 3-4 hours.

3. The method for preparing the polyimide film according to claim 1, characterized in that, In step S2, the molar amounts of 4,4'-diaminobenzophenone and 3,3',4,4'-benzophenone tetracarboxylic dianhydride are the same; The conditions for the polycondensation reaction include: a polycondensation temperature of 75-85°C and a polycondensation time of 5-7 hours.

4. The method for preparing the polyimide film according to claim 1, characterized in that, In step S2, N,N-dimethylformamide is added to bring the solid content of the reaction system to 18-22 wt%.

5. The method for preparing the polyimide film according to claim 1, characterized in that, In step S3, the crosslinking agent is 1,3,5-tris(4-aminobenzene)benzene; The catalyst is triethylamine; The dehydrating agent is propionic anhydride.

6. The method for preparing the polyimide film according to claim 1, characterized in that, In step S3, the molar amount of the crosslinking agent is 1.5 to 2.5% of the total molar amount of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 4,4'-diaminobenzophenone; The molar ratio of the crosslinking agent, catalyst, and dehydrating agent is 0.1~0.2:1:0.4~0.

6.

7. The method for preparing the polyimide film according to claim 1, characterized in that, In step S3, the conditions for the chemical imidization reaction include: the temperature of the chemical imidization reaction is 20~30℃, and the time of the chemical imidization reaction is 10~14h.

8. The method for preparing the polyimide film according to claim 1, characterized in that, In step S3, the mixing step includes: adding the crosslinking agent to the polyamic acid precursor solution and reacting for 0.5 to 1.5 hours, followed by adding the catalyst and dehydrating agent.

9. The method for preparing the polyimide film according to claim 5, characterized in that, In step S4, the drying conditions include: maintaining a temperature of 70–90°C for 10–15 minutes; The pre-curing conditions include: holding at 140–160°C for 25–35 minutes; The curing conditions include: holding at 170–190°C for 25–35 minutes.

10. The polyimide film prepared by the method of any one of claims 1-9, characterized in that, The polyimide film has a 5wt% thermal weight loss temperature ≥570℃ and a carbon residue rate ≥60wt% under nitrogen atmosphere at 800℃.